Typical September weather
Chicago
Illinois · September
76° days
57° nights
about 6 rainy days · 12½ hours of daylight · lake 69°
What to pack
- Light jacket
- Sunscreen
What September feels like
Ask anyone who lives here and September comes up first: the lake holds its summer warmth, the crowds vanish after Labor Day, and the neighborhood festivals keep going. Nights turn properly cool, so that rooftop reservation wants a jacket.
Expect about 6 days with real rain — enough to notice, not enough to plan around. Humidity stays comfortable; the air never feels heavy.
Can you swim?
The lake runs about 69° — brisk but swimmable.
The numbers
| Typical high | 76° |
|---|---|
| Typical low | 57° |
| Days with real rain | 6 |
| Total rain | 3.2 in |
| Humidity | comfortable |
| Water temperature | 69° |
| Sunrise / sunset (mid-month) | 6:31 am / 7:00 pm |